1. Field of the Invention
This invention relates to a solid drug preparation containing a powder microdose drug coated with wax.
Since the drug preparation of this invention is excellent in content uniformity, it has a high practical value as a microdose drug preparation which exhibits the effect of medicine by a microdose of it. The preparation of this invention contains a stabilized drug and hence is suitable as a microdose drug preparation which does not encounter the reduction in crystallinity of an effective component therein and the reduction in the stability of the effective component during the production or storage of the preparation.
2. Description of the Prior Art
The content uniformity of a solid drug preparation gives almost no problem in a preparation having a large content of drug per unit of the preparation, i.e., a large content of drug per tablet, capsule or unit dose of the package but it becomes serious in case of a microdose drug having a drug content of less than 50 mg, particularly less than a few milligrams. For the preparation of a microdose drug, there are a practiced method (solution method) wherein a solution of a drug dissolved in a proper solvent is uniformly dispersed in excipient and then the dispersion is formed into a preparation and a method (powder dilution method) wherein a drug is compounded with an excipient in the form of the powder dilution and then the resulting product is formed into a preparation.
In the powder dilution method, since it is frequently difficult to produce drug preparations having excellent drug content uniformity by an ordinary step or, in particular, it is difficult to uniformly mix aggregates of the drug with excipients, a homogenizing step such as mixture pulverization, etc., is required and hence for obtaining a uniformity of drug content, complex manufacturing procedures are required. The solution method may be superior to the powder dilution method in the point of uniformity in drug content but in the solution method there is pointed out such difficulties that since a drug is dissolved in a solvent during the production of preparations, the crystal form changes, for example, a hydrate changes into a solvate to change the drug itself and also when the solution is dispersed in excipient, the particle size of the drug is reduced. The stability of the drug to the passage of time is thus reduced. It is very important for the preparations of extremely low dose drugs having a drug content of less than 1 mg per unit of the preparation to assure the drug content uniformity and the stability of the effective component. Since the extremely low dose drugs generally have strong medicinal activity, if the uniformity of drug content and the stability of effective component are not strictly assured, there is a possibility that the desired medicinal effect is not obtained or an unforeseen accident by overdose may occur.